问题描述
我在Swift中遇到了这个设计问题。这是我的根类及其子类:
enum VisualItemType {
case video,picture,text,...
}
class VisualItem {
public var itemType: VisualItemType
...
}
class PictureItem:VisualItem {
private var subItems:[PictureItem OR TextItem But NOT VideoItem]? //Overlay of picture can be picture or text but not video
}
class VideoItem: VisualItem {
private var subItems:[VisualItem]? //Overlay of video can be any type of visual item
}
如何在Swift中完全实现PictureItem的子项而不创建新的子类型枚举?
解决方法
您可以通过引入只有TextItem
和PictureItem
符合的新协议来做到这一点:
protocol PictureOverlayable: VisualItem {}
class TextItem: VisualItem,PictureOverlayable {}
class PictureItem: VisualItem,PictureOverlayable {
private var subItems: [PictureOverlayable]?
}